The present invention relates to an EL sheet for information appliances and others which may be used in high-temperature environments and in which lead electrodes of the EL sheet may receive great force while in use.
One example of conventional EL sheets comprises a transparent substrate of polyethylene terephthalate (hereinafter referred to as “PET”) with a transparent electrode layer of indium tin oxide (hereinafter referred to as “ITO”) formed thereon, and this is cut into a tabular structure with lead electrodes protruding from it. On the ITO layer of this tabular structure, formed is an EL element that comprises multiple layers mentioned below. A phosphor-containing light-emitting layer, an insulating layer, a back electrode layer and a protective layer are printed on the ITO layer. A lead electrode running from the transparent electrode layer is electrically connected to the ITO layer. On the other hand, a lead electrode running from the back electrode layer is formed as follows: A resist layer is formed on the ITO layer, and the lead electrode for the back electrode layer is formed while the back electrode layer is printed on the ITO layer. In case where the lead electrodes are electrode plates of metal, an electroconductive adhesive is printed on every lead electrode, and an electrode plate of metal is put on each lead electrode via the adhesive therebetween, and is thermally fixed to it under pressure. In another example of conventional EL sheets, a metal chip to be an electrode is kept in contact with every lead electrode, and the lead electrodes are sealed up along with the EL element by covering them with a protective layer while the tip of each metal chip is made to protrude outside, and thereafter the protruding tip of each metal chip is folded to complete the individual electrode plates.
The first example of the prior-art technique mentioned above is problematic in that its electric reliability is low. For example, when the ambient temperature around it is 80° C. or higher or when some strong external force is given to the lead electrodes, the bonding parts will peel to cause electric connection failure. The second example mentioned above is also problematic since the contact between the lead electrodes and the electrode chips is unstable and the contact pressure between them is difficult to keep all the time constant. In addition, the material of the transparent substrate, PET will be deformed by creeping, and it could not be stably contacted with electrode chips when exposed to temperature change or when given repeated stress, and further, the contact area may rust to cause electric connection failure.